The present inventi on relates to a ball ring unit for a seat belt pretensioner and a process for the manufacture of a ball ring unit.
In seat belt systems. with seat belt pretensioners it is necessary to avoid a reverse movement of the seat belt after the pretensioning process. To this end, reverse movement locks are used in present seat belt systems. A reverse movement lock disclosed in U.S. Pat. No. 5,519,997 is formed by a ball ring that is located on a cone connected to the piston of the seat belt pretensioner inside a belt tightening tube. During the pretensioning process the balls are moved in the direction of the tapering space and dig into the inner wall of the belt tightening tube and the outer wall of the cone. As a result, a reverse movement of the piston and therefore a loosening of the seat belt is reliably avoided.
In the solution outlined above, the assembly of the locking balls has proved to be difficult. As the locking balls have to be inserted individually in the intermediate space between the cone and the inner wall of the belt tightening tube, this process is time consuming and expensive.
By providing a covering or sheath the balls or locking balls can be combined to form a subassembly xe2x80x9cball ring unitxe2x80x9d before assembly of the balls. As a result the ball ring unit can be slid onto the cone of a reverse movement lock simply and in an extremely short period of time.
There is provided in accordance with the present invention a ball ring for a seat belt pretensioner comprising a plurality of locking balls arranged in a ring, the ring of locking balls having a covering that combines the locking balls to form a module.